Although deaths caused by infections have decreased dramatically in Japan through the improvement in public health and the discovery of antibiotics and the like following the Second World War, the incidences of lifestyle diseases and particularly cancer have continued to increase in their place, with cancer having become the leading cause of death amongst Japanese in 1981. At present, about one out of every three persons dies of cancer. In addition, cancer is rapidly proliferating not only in Japan but in other countries as well, and is a disease that can be considered to be a common enemy of all persons.
Thus, the development of methods for preventing or treating tumors including cancer is considered to be an important and critical issue.
In actuality, although various anticancer drugs have been developed and are currently in use as therapeutic drugs, these have numerous problems, including the occurrence of serious adverse side effects.
With respect to acacia, acacia honey is known, and tannin which is extracted from bark thereof is known to be able to be used as a tanning agent or wood adhesive, while more recently, extracts of genus Acacia have been disclosed to have selective inhibitory effects on COX-2 (Patent Document 1), and bark of genus Acacia has been disclosed to have active oxygen elimination effects (Patent Document 2) and skin whitening effects due to the effect of inhibiting tyrosinase activity (Patent Document 3). However, acacia bark and polyphenols derived from acacia bark have heretofore not been confirmed to have an antitumor action.    [Patent Document 1] JP 2004-532811 A    [Patent Document 2] JP 2004-352639 A    [Patent Document 3] JP 10-025238 A